Definition: The associative property states that you can add or multiply regardless of how the numbers are grouped. By 'grouped' we mean 'how you use parenthesis'.
When you are having difficulty breathing, or your chest is tight, or when you are wheezing, Ventolin Rotacaps open up the breathing tubes in your lungs to help with breathing. Because the medicine in your Ventolin Rotacaps gives fast relief from your chest symptoms, it is often called a 'reliever'.
ACP stands for Automatic Colt Pistol. Essentially, it meant the cartridge was a short cased, auto-loading pistol round developed for use originally in Colt's (then at the time) new automatic pistols. .45 ACP is also known as .45 Auto. I'm not a Glock fan so I don't know the second part of your question.